A study on lattice parameters of martensite in Ni–Ti–Ta shape memory alloys

The lattice parameters of B19′ martensite in Ni–Ti–Ta shape memory alloys are analyzed by means of the X-ray diffraction (XRD), the selected area diffraction patterns (SADPs) of transmission electron microscopy (TEM) and the multiphase Rietveld methods. Experimental results indicate that when the Ni content is constant, the lattice parameters a and c, monoclinic angle β and unit cell volume V increase, while lattice parameter b decreases with increasing Ta content; when the Ta content is constant, the lattice parameters a and c, monoclinic angle β and unit cell volume V increase, while lattice parameter b decreases with increasing Ni content. With the unit cell volume V increased, the R factor and the aberration of unit cell increase.